A novel Mo(V) diphosphate with an intersecting tunnel structure: Sr(MoO)2(P2O7)2

A novel Mo(V) diphosphate Sr(MoO)₂P₂O₇ has been synthesized. It crystallizes in the space group P2₁/n with a=7.925(1) Å, b=7.739(1) Å, c=9.485(1) Å and β=91.05(1)°. Its original framework consists of MoP₂O₁₁ units built up of one P₂O₇ group sharing two apices with one MoO₆ octahedron. The MoP₂O₁₁ units share corners, forming [MoP₂O₁₀]_∞ chains running along [101]. The assemblage of these chains forms the [Mo₂P₄O₁₆]_∞ intersecting tunnel framework. The Sr²⁺ cations are located at the tunnel intersection, showing a distorted cubic coordination. This structure is compared to those of Ba(MoO)₂P₂O₇ and LiMoOP₂O₇, which are also built up of MoP₂O₁₁ units forming [MoP₂O₁₀]_∞ chains, but with different configurations.     

Discovery Learning Using Chemland Simulation Software

We describe in this paper a set of computer-based simulations for use in general chemistry courses. We detail a discovery-based method of teaching, whereby students are led to discover concepts through guided-inquiry use of the simulation modules. Three methods of using the software are described, as is the development process we have employed. Finally, we describe our evaluation studies of the effects of our methodology and the use of a scientific reasoning instrument. The software is available free for download as part of this article.     

Benzyl tert‐but­oxy­carbonyl‐α‐amino­isobutyrate

The small synthetic peptide, benzyl 2‐(tert‐but­oxy­carbonyl‐amino)­isobutyrate, C₁₆H₂₃NO₄, has the α‐helical conformation [|?| = 55.8 (2)° and |ψ| = 37.9 (2)°] observed in peptide fragments of peptaibols containing the α‐amino­isobutyric acid (Aib) residue. The structure shows no intramolecular hydrogen bonding, which would disrupt the limited conformational freedom associated with this amino acid. Two weak intermolecular hydrogen contacts are observed.     

Electrodynamics of Noble Metal Nanoparticles and Nanoparticle Clusters

In this paper we examine the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surface-enhanced Raman (SER) intensities. The particles and clusters are chosen to be representative of what has been studied in recent work on colloids and with lithographically prepared particles. These include spheres, spheroids, truncated tetrahedrons, and clusters of two or three of these particles, with sizes that are too large to be described with simple electrostatic approximations but small compared to the wavelength of light. The electrodynamics calculations are mostly based on the discrete dipole approximation (DDA), which is a coupled-finite element approach which produces exact or nearly exact results for particles of arbitrary size and shape if fully converged. Mie theory results are used to study the validity of the DDA for spherical particles, and we also study the validity of the modified long wavelength approximation (MLWA), which is based on perturbative corrections to the electrostatic limit, and of the single dipole per particle approximation (SDA). The results show how the dipole plasmon resonance properties and the electric field contours around the particle vary with particle shape and size for isolated particles. For clusters of particles, we study the effect of interparticle spacing on plasmon resonance characteristics. We also show that the quadrupole resonance is much less sensitive to particle shape and interparticle interactions than the dipole plasmon resonance. These results provide benchmarks that will be used in future comparisons with experiment.     

Studies on pyrrolidinone. Synthesis of aza analogs of podophyllotoxin and related compounds

The Friedel-Crafts cyclisation of N-benzhydrylpyroglutamic acids whose aromatic rings are substituted by methoxy or methylenedioxy groups gives podophyllotoxin analogs whose lactone ring was changed to a lactam.     

Laboratory and field measurements of a badge type passive sampler for the determination of ambient sulfur dioxide concentrations

The performance of a badge type passive sampler for the determination of sulfur dioxide is described. The trapping agent is triethanolamine. Analysis is performed by ion chromatography. Thus, the method allows the simultaneous detection of sulfur dioxide and nitrogen dioxide. The sampler was tested in the laboratory and in the field. The intercomparison with independent methods in the field showed very good agreement against two active sampling methods. Regression analyses (the results of the passive sampler always represent the y-axes) gave r² = 0.81 and k = 1.07 ± 0.01 for the intercomparison with an annular denuder technique and r² = 0.92 and k = 0.96 ± 0.01 for the intercomparison with a commercial fluorescence sulfur dioxide analyzer. The average reproducibility in the field was 7% (RSD). The detection limit was 0.18 μg SO₂/m³ for an exposure time of two weeks. Received: 9 February 1998 / Revised: 22 June 1998 / Accepted: 26 June 1998     

LCP aromatic polyesters by esterolysis melt polymerization

Polyarylates have previously been synthesized from acetate esters via esterolysis (loss of methyl acetate). This polycondensation can be extended to p‐substituted aromatic monomers for liquid crystal polyesters (LCPs). For AB‐type polymers, methyl p‐acetoxybenzoate and methyl 6‐acetoxynaphthoate were copolymerized to an LCP with reasonable molecular weights. Benzoate esters, methyl 4‐benzoyloxybenzoate (MBB) and methyl 6‐benzoyloxy‐2‐naphthoate (MBN), are also investigated. Several tin and antimony oxide catalysts were effective. The rate of esterolysis polymerization of MBB and MBN is slower than that of the corresponding acidolysis melt polymerization, but fast enough to give relatively high‐molecular‐weight polymers and similar thermal stability as commercial LCP prepared by acidolysis. Using these alternative benzoyloxy groups significantly reduced the color problem, because ketene loss cannot occur. Esterolysis melt polymerizations leading to AB/AABB‐type LCPs were performed using either dimethyl 2,6‐naphthalene dicarboxylate (DMND) or dimethyl terephthalate (DMT) with methyl 4‐acetoxybenzoate and phenylhydroquinone diacetate with tin and antimony catalysts. DMT‐based monomer compositions show much faster polymerization than DMND‐based compositions using antimony oxide catalyst. All these LCPs show a T_g in the 140–170 °C range as a result of the inclusion of the naphthalene and/or phenyl hydroquinone units in the polymer chain. Compositions completely off‐balanced on either side still lead to relatively high‐molecular‐weight copolyesters because either excess monomer can be removed during polymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3586–3595, 2000     

ZrIV‐ und TaV‐Komplexe mit methanoverbrückten Bis(aryloxy)‐Liganden

Zr^IV and Ta^V Complexes with Methano‐Bridged Bis(aryloxy) Ligands The bis(aryloxy) ligand precursor compounds bis(2‐trimethylsiloxy‐5‐tbutylphenyl)methane (L–SiMe₃) and its bromoderivative (2‐trimethylsiloxy‐3‐bromo‐5‐tbutylphenyl)(2′‐trimethylsiloxy‐5′‐tbutylphenyl)methane (L^Br–SiMe₃) are prepared in analogy to the corresponding calixarenes in excellent yields. X‐ray structure analysis for L^Br–SiMe₃: space group P2₁/c, a = 12.462(7), b = 10.466(6), c = 23.315(14) Å, β = 105.02(4)°, V = 2937(3) ų, Z = 4. L–SiMe₃ and L^Br–SiMe₃ react with Zr^IV and Ta^V chlorides in very good yields forming di‐ and trinuclear complexes. From the reaction of CpZrCl₃ with L^Br–SiMe₃ in the ratio of 3 : 2 a Zr₃ complex ( 7 ) is obtained, with one L^Br ligand only, which Zr atoms are bridged by a μ₃‐oxygen. The X‐ray structure analysis of 7 (space group R 3, a = 33.23(6), c = 24.47(8) Å, V = 23405(128) ų, Z = 18) additionally reveals that one phenolato oxygen atom of the L^Br ligand is terminally bound to a distorted tetragonal‐pyramidal coordinated Zr atom, while the second phenolato oxygen atom of the L^Br ligand forms a bridge to another Zr atom with a distorted octahedral coordination. The third Zr atom is also found in a distorted octahedral coordination mode. The reactions of L–SiMe₃ and L^Br–SiMe₃ with CpTaCl₄ and TaCl₅ yield dinuclear Ta complexes with a bridging bis(aryloxy) ligand. NMR spectroscopic data point out that the coordination of the bis(aryloxy) ligands in the Ta complexes very much resembles that in the Zr₃‐complex with one terminal and one bridging phenolato oxygen atom. The Zr₃ and the Ta complexes L^BrTa₂Cp₂Cl₆ and LTa₂Cl₈ were tested with respect to their catalytic properties in olefin polymerisation reactions in the presence of MAO.